Development and characterization of octreotide-modified curcumin plus docetaxel micelles for potential treatment of non-small-cell lung cancer.

We prepared octreotide (OCT)-modified curcumin plus docetaxel micelles to enhance active targeting and inhibit tumor metastasis by destroying vasculogenic mimicry (VM) channels. Soluplus was applied as an amphiphilic material to form micelles via film dispersion. The cytotoxic effects, active cellular targeting, and inhibitory effects on metastasis were systematically evaluated in vitro using A549 cells, and in vivo antitumor effects were evaluated using xenograft tumor-bearing mice. In vitro assays indicated that the OCT-modified curcumin plus docetaxel micelles showed robust cytotoxicity on A549 cells and effectively inhibited VM channels and tumor metastasis. Studying the mechanism of action indicated that OCT-modified curcumin plus docetaxel micelles downregulated MMP-2 and HIF-1α. In vivo assays indicated that OCT-modified curcumin plus docetaxel micelles increased drug accumulation at tumor sites and showed obvious antitumor efficacy. The developed OCT-modified curcumin plus docetaxel micelles may offer a promising treatment strategy for non-small-cell lung cancer.

Eficacia y seguridad del octreotide asociado a nutrición parenteral total en el tratamiento conservador del quilotórax / Efficacy and safety of adjuvant octreotide with parenteral nutrition for conservative treatment of chylothorax

No disponible

Somatostatin-receptor-based imaging and therapy of gastroenteropancreatic neuroendocrine tumors.

Somatostatin receptor imaging (SRI) with [(111)In-DTPA(0)]octreotide has proven its role in the diagnosis and staging of gastroenteropancreatic neuroendocrine tumors (GEPNETs). Newer radiolabeled somatostatin analogs which can be used in positron emission tomography (PET) imaging, and which have a higher affinity for the somatostatin receptor, especially receptor subtype-2, have been developed. It would be desirable, however, if one radiolabeled analog became the new standard for PET imaging, because the current application of a multitude of analogs implies a fragmented knowledge on the interpretation of the images that are obtained in clinical practice. In our view, the most likely candidates for such a universal PET tracer for SRI are [(68)Ga-DOTA(0),Tyr(3)]octreotate or [(68)Ga-DOTA(0),Tyr(3)]octreotide. Treatment with radiolabeled somatostatin analogs is a promising new tool in the management of patients with inoperable or metastasized neuroendocrine tumors. Symptomatic improvement may occur with all (111)In-, (90)Y-, or (177)Lu-labeled somatostatin analogs that have been used for peptide receptor radionuclide therapy (PRRT). The results that were obtained with [(90)Y-DOTA(0),Tyr(3)]octreotide and [(177)Lu-DOTA(0),Tyr(3)]octreotate are very encouraging in terms of tumor regression. Also, if kidney protective agents are used, the side effects of this therapy are few and mild, and the median duration of the therapy response for these radiopharmaceuticals is 30 and 40 months respectively. The patients' self-assessed quality of life increases significantly after treatment with [(177)Lu-DOTA(0),Tyr(3)]octreotate. Lastly, compared to historical controls, there is a benefit in overall survival of several years from the time of diagnosis in patients treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate. These data compare favorably with the limited number of alternative treatment approaches. If more widespread use of PRRT can be guaranteed, such therapy may well become the therapy of first choice in patients with metastasized or inoperable GEPNETs.

Reducing renal uptake of 111In-DOTATOC: a comparison among various basic amino acids.

PURPOSE: Several studies have reported significant renal toxicity after the use of a high dose of 90Y-DOTATOC. Thus, renal protection is necessary in treatments with 90Y-DOTA Tyr3-octreotide (DOTATOC). The infusion of certain positively charged amino acids has been shown to effectively reduce renal uptake of DOTATOC. In this study, we compared the effectiveness of three kinds of amino acids, D-lysine (lysine), L-arginine (arginine) and histidine, on renal protection in healthy rats and tried to determine which one was the most effective. METHODS: Twenty SD healthy male rats were divided into 4 groups: lysine, histidine, arginine, and control. The rats were injected with a dose of 400 mg/kg of amino acid or 2 ml of phosphate-buffered saline (PBS) (as control) intraperitoneally. All rats were sacrificed at 4 hrs after the injection of 1 MBq 111In-DOTATOC. Samples of the kidney were taken and weighed carefully. The counts of radioactivity were measured by a gamma counter and renal concentrations were calculated and expressed as percent injected dose per gram (% ID/g). RESULTS: The renal uptake of 111In-DOTATOC was significantly lower for all three kinds of amino acids when compared to the control group. The renal uptake of 111In-DOTATOC in the lysine group was significantly lower than those in the histidine and arginine groups. The renal uptake of 111In-DOTATOC in the histidine group was lower than that in the arginine group, but no statistical difference was noted. CONCLUSION: Among these three amino acids, lysine had the best reduction rate of renal uptake of DOTATOC. Histidine was more effective than arginine but no statistical difference was noted.

Pre-clinical evaluation of 2,3-dimercaptosuccinic acid as a radiation nephrotoxicity protective agent during radiopeptide therapy of neuroendocrine malignancy.

AIM: To determine if dimercaptosuccinic acid (DMSA), an agent originally developed as a safe non-toxic antidote for heavy metal poisoning, would be useful as a kidney radiation dose reduction agent in patients undergoing radiopeptide therapy for cancer. METHODS: Thirty-six adult male Wistar rats were injected via the penile vein with 10 MBq of 177Lu-DOTA-tyr(3)-octreotate. At 30 min after the radiopeptide injection, 18 of the animals (intervention group) were injected with 0.15 mg x g(-1) of DMSA (i.p.). Samples were collected for gamma counting at 24 (n=12), 48 (n=12) and 72 h (n=12) after administration of the radiopeptide. At each time point, the percentage injected dose per gram of tissue in each sample of the six control animals was compared with that of the six animals from the DMSA injection regimen. RESULTS: The i.p. injection of 0.15 mg x g(-1) of DMSA 30 min following the administration of the 177Lu-DOTATATE reduced the mean (95% CI) kidney retention of radiopeptide by 15.6% (2.6-24.6) at 72 h while not significantly affecting uptake in other organs. Statistical testing of the difference between the two groups of animals (DMSA versus controls) at 72 h post-administration of the radiopeptide indicated only a 3% chance that the magnitude of the reduction in kidney radiopeptide retention observed would be expected due to natural variation (i.e., if there was no difference between the groups). CONCLUSION: This study has indicated that DMSA has the potential to selectively reduce radiopeptide kidney retention. Further work is necessary to determine the most effective dose of DMSA and the most effective timing regimen, and to examine the clinical efficacy of several other chelating agents.

Potential increased tumor-dose delivery with combined 131I-MIBG and 90Y-DOTATOC treatment in neuroendocrine tumors: a theoretic model.

UNLABELLED: (131)I-Metaiodobenzylguanidine (MIBG) and (90)Y-DOTA-D-Phe1-Tyr3-octreotide (DOTATOC) have been used as radiotherapeutic agents for treating neuroendocrine tumors. The tumor dose delivered by these agents is often insufficient to control or cure the disease. However, these 2 agents used together could potentially increase tumor dose without exceeding the critical organ dose because the dose-limiting tissues are different. In this paper, we investigate the conditions in which combined-agent therapy is advantageous and we quantify the expected tumor-dose gain. METHODS: A series of equations was derived that predicted the optimal combination of agents and the fractional increase in tumor dose available from combined-agent therapy with respect to either (131)I-MIBG or (90)Y-DOTATOC. The results obtained from these derivations were compared with direct dose calculations using published dosimetric organ values for (131)I-MIBG and (90)Y-DOTATOC along with critical organ-dose limits. Tumor dose was calculated as a function of the tumor-dose ratio, defined as the (90)Y-DOTATOC tumor dose per megabecquerel divided by the (131)I-MIBG tumor dose per megabecquerel. Comparisons were made between the dose delivered to tumor with single-agent therapy and the dose delivered to tumor with combined-agent therapy as a function of the tumor-dose ratio and the fraction of activity contributed by each agent. RESULTS: The dose model accurately predicted the optimal combination of agents, the range at which combined-agent therapy was advantageous, and the magnitude of the increase. For the published organ dosimetry and critical organ-dose limits, combined-agent therapy increased tumor dose when the tumor-dose ratio was greater than 0.67 and less than 5.93. The maximum combined-agent tumor-dose increase of 68% occurred for a tumor-dose ratio of 2.57, using 92% of the maximum tolerated (90)Y-DOTATOC activity supplemented with 76% of the maximum tolerated activity of (131)I-MIBG. Variations in organ dose per megabecquerel and dose-limiting values altered both the magnitude of the increase and the range at which combined-agent therapy was advantageous. CONCLUSION: Combining (131)I-MIBG and (90)Y-DOTATOC for radiotherapy of neuroendocrine tumors can significantly increase the delivered tumor dose over the dose obtained from using either agent alone. Prior knowledge of the normal-organ and tumor dosimetry of both agents is required to determine the magnitude of the increase.

[(99m)Tc]Demotate 2 in the detection of sst(2)-positive tumours: a preclinical comparison with [(111)In]DOTA-tate.

PURPOSE: The aim of this study was to evaluate [(99m)Tc]Demotate 2 ([(99m)Tc-N(4) (0-1),Asp(0),Tyr(3)]octreotate) as a candidate for in vivo imaging of sst(2)-positive tumours and to compare it with [(111)In]DOTA-tate ([(111)In-DOTA(0),Tyr(3)]octreotate). METHODS: Labelling of Demotate 2 with (99m)Tc was performed at room temperature using SnCl(2) as reductant in the presence of citrate at alkaline pH. Radiochemical analysis involved ITLC and HPLC methods. Peptide conjugate affinities for sst(2) were determined by receptor autoradiography on rat brain cortex sections using [DOTA(0),(125)I-Tyr(3)]octreotate as the radioligand. The affinity profile of Demotate 2 for human sst(1)-sst(5) was studied by receptor autoradiography in cell preparations using the universal somatostatin radioligand [(125)I][Leu(8),(D: )Trp(22),Tyr(25)]somatostatin-28. The internalisation rates of [(99m)Tc]Demotate 2 and [(111)In]DOTA-tate were compared in sst(2)-positive and -negative control cell lines. Biodistribution of radiopeptides was studied in male Lewis rats bearing CA20948 tumours. RESULTS: Peptide conjugates showed selectivity and a high affinity binding for sst(2) (Demotate 2 IC(50)=3.2 nM and DOTA-tate IC(50)=5.4 nM). [(99m)Tc]Demotate 2, like [(111)In]DOTA-tate, internalised rapidly in all sst(2)-positive cells tested, but not in sst(2)-negative control cells. After injection in CA20948 tumour-bearing rats both radiopeptides showed high and specific uptake in the sst(2)-positive organs and in the implanted tumour and rapid excretion from non-target tissues via the kidneys. CONCLUSION: [(99m)Tc]Demotate 2, similarly to the known sst(2)-targeting agent [(111)In]DOTA-tate, showed promising biological qualities for application in the scintigraphy of sst(2)-positive tumours.

Preclinical evaluation of the breast cancer cell-binding peptide, p160.

PURPOSE: Selective delivery of drugs into the target tissue is expected to result in high drug concentrations in the tissue of interest and therefore enhanced drug efficacy. To develop a peptide-based radiopharmaceutical, we investigated the properties of a peptide with affinity for human breast cancer, which has been selected through phage display. EXPERIMENTAL DESIGN: The bioactivity of the p160 peptide (VPWMEPAYQRFL) was evaluated in vitro and in vivo. The specific binding to human breast cancer MDA-MB-435 cells was confirmed in competition experiments. Internalization of the peptide was investigated with confocal microscopy. Furthermore, the biodistribution of (131)I-labeled p160 was studied in tumor-bearing mice. In vivo stability was evaluated at different periods after tracer administration using high-performance liquid chromatography analysis. RESULTS: The binding of (125)I-labeled p160 was inhibited up to 95% by the unlabeled peptide with an IC(50) value of 0.6 micromol/L. In addition, 40% of the total bound activity was found to be internalized into the human breast cancer cells. Although a rapid degradation was seen, biodistribution studies in nude mice showed a higher uptake in tumor than in most of the organs. Perfusion of the animals caused a reduction of the radioligand accumulation in the healthy tissues, whereas the tumor uptake remained constant. A comparison of [(131)I]p160 with a (131)I-labeled Arg-Gly-Asp peptide revealed a higher tumor-to-organ ratio for [(131)I]p160. CONCLUSIONS: p160 has properties that make it an attractive carrier for tumor imaging and the intracellular delivery of isotopes or chemotherapeutic drugs.

111In-labelled somatostatin analogues in a rat tumour model: somatostatin receptor status and effects of peptide receptor radionuclide therapy.

PURPOSE: Peptide receptor scintigraphy with the radioactive somatostatin analogue 111In-DTPA-octreotide is a sensitive and specific technique to show in vivo the presence of somatostatin receptors on various tumours. Since 111In emits not only gamma rays but also therapeutic Auger and internal conversion electrons with a medium to short tissue penetration (0.02-10 microm and 200-550 microm, respectively), 111In-DTPA-octreotide is also being used for peptide receptor radionuclide therapy (PRRT). In this study we investigated the therapeutic effects of 111In-DTPA-octreotide in tumours of various sizes. Regrowth of a tumour despite PRRT with 111In-DTPA-octreotide may be due to the lack of crossfire from 111In, whereby any possible receptor-negative tumour cell can multiply. We therefore also investigated the somatostatin receptor status of the tumour before and after PRRT. METHODS: The radiotherapeutic effects of different doses of 111In-DTPA-octreotide in vivo were investigated in Lewis rats bearing small (< or = 1 cm2) or large (> or = 8 cm2) somatostatin receptor-positive rat pancreatic CA20948 tumours expressing the somatostatin receptor subtype 2 (sst2). In addition, the somatostatin receptor density on the tumour after injection of a therapeutic labelled somatostatin analogue was investigated when the tumour was either declining in size or regrowing after an initial reduction in size. To initiate a partial response of the tumour (so that regrowth would follow) and not a complete response, a relatively low dose was administered. RESULTS: Impressive radiotherapeutic effects of 111In-labelled octreotide were observed in this rat tumour model. Complete responses (up to 50%) were found in the animals bearing small (< or 1 cm2) tumours after at least three injections of 111 MBq or a single injection of 370 MBq 111In-DTPA-octreotide, leading to a dose of 6.3-7.8 mGy/MBq (1-10 g tumour). In the rats bearing the larger (> or = 8 cm2) tumours, the effects were much less pronounced and only partial responses were achieved in these groups. Clear sst2 expression was found in the control as well as in the treated tumours. A significantly higher tumour receptor density (p<0.001) was found when the tumours regrew after an initial decline in size after low-dose PRRT in comparison with the untreated tumours. CONCLUSION: Therapy with 111In-labelled somatostatin analogues is feasible but should preferably start as early as possible during tumour development. One might also consider the use of radiolabelled somatostatin analogues in an adjuvant setting after surgery of somatostatin receptor-positive tumours in order to eradicate occult metastases. We showed that PRRT led to an increase in the density of somatostatin receptors when the tumours regrew after an initial decline in size because of PRRT. Upregulation of the somatostatin receptor may lead to higher uptake of radiolabelled peptides in therapeutic applications, which would probably make repeated injections of radiolabelled peptides more effective.

PEGylation of octreotide: II. Effect of N-terminal mono-PEGylation on biological activity and pharmacokinetics.

PURPOSE: : To determine the optimal polyethylene glycol (PEG)-conjugate of octreotide by evaluating the effects of PEGylation chemistry on the biological activity and pharmacokinetic properties. METHODS: : Octreotide was chemically modified by reaction with succinimidyl propionate monomethoxy PEG (SPA-mPEG, molecular weight 2000) or succinimidyl butyraldehyde-mPEG (ALD-mPEG, molecular weight 2000 and 5000). The structural conformation of PEG-octreotides was evaluated by circular dichroism (CD), the biological activity was assessed by measuring the decrease of serum insulin-like growth factor-I levels in rats, and a pharmacokinetic study was performed after subcutaneous administration in rats. The stability against acylation was investigated with poly(D,L -lactide-co-glycolide) (PLGA). RESULTS: : ALD-mPEG was site-specific in PEGylating octreotide at the N-terminus. The mono-PEG-octreotides prepared with ALD-mPEG (mono-ALDPEG-octreotide), which alkyl bond preserves the amine's positive charge, showed complete preservation of biological activity, whereas the PEG-octreotides prepared with SPA-mPEG showed lower activity. In the CD analysis, the spectra of the mono-ALDPEG-octreotides were nearly superimposable with that of native octreotide. The mono-ALDPEG-5K-octreotide showed significantly improved pharmacokinetic properties compared with mono-ALDPEG-2K-octreotide as well as native octreotide. Both mono-ALDPEG-2K- and mono-ALDPEG-5K-octreotides were stable against acylation by degrading PLGA. CONCLUSIONS: : The mono-PEGylation of octreotide at N-terminus with ALD-mPEG produced a conjugate that is biologically and structurally active and stable against acylation by PLGA, and therefore it may serve as a candidate for somatostatin microsphere formulations.

Preclinical evaluation of new and highly potent analogues of octreotide for predictive imaging and targeted radiotherapy.

PURPOSE: Molecular imaging and targeted radiotherapy are emerging fields in nuclear oncology. Five human somatostatin receptors (hsstr1-hsstr5) are known to be overexpressed to some degree on various tumors, sstr2 being the most important one. Clinically used somatostatin based radiopeptides target exclusively sstr2. The aim of this study was to develop novel analogues with a broader sstr profile for diagnostic (positron emission tomography and single-photon emission computed tomography) and radiotherapeutic applications. EXPERIMENTAL DESIGN: The following promising structures emerged from a parallel synthetic approach: [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA(0)),1-Nal(3),Thr(8)]-octreotide (1, DOTA-NOC-ATE) and [DOTA(0),BzThi(3),Thr(8)]-octreotide (2, DOTA-BOC-ATE). The conjugates were labeled with cold and radioactive (111)In. Pharmacologic properties were compared with [(111)In-DOTA,Tyr(3)]-octreotide ([(111)In-DOTA]-TOC). RESULTS: The receptor affinity profile showed high affinity of both peptides to hsstr2, hsstr3, and hsstr5 and some intermediate affinity to hsstr4, whereas [(111)In-DOTA]-TOC shows affinity only to sstr2. The internalization is fast in sstr2 expressing AR4-2J and in transfected sstr3 expressing human embryonic kidney 293 cells. Both radiopeptides internalize much more efficiently than [(111)In-DOTA]-TOC. Animal biodistribution studies showed very high and specific uptake of [(111)In]-1 and [(111)In]-2 in s.c. implanted AR4-2J tumors (Lewis rats) and in somatostatin receptor expressing normal tissues. The uptake was at least 2-fold higher in these tissues and in the tumor compared with [(111)In-DOTA]-TOC. In addition, the kidney uptake was significantly lower for both radiopeptides. CONCLUSIONS: These data suggest that the novel radiopeptides are superior to [(111)In/(90)Y-DOTA]-TOC and show great promise for the clinical application in the imaging of somatostatin receptor-positive tumors and their targeted radiotherapy.

A stylized computational model of the rat for organ dosimetry in support of preclinical evaluations of peptide receptor radionuclide therapy with (90)Y, (111)In, or (177)Lu.

UNLABELLED: The therapeutic effects of peptide receptor-based radionuclide therapy are extensively being investigated in rats bearing tumors. Both the dose to the tumor and the therapy-limiting dose to normal tissues, such as kidneys and bone marrow, are of interest for these preclinical studies. The aim of this work was to develop a generalized computational model for internal dosimetry in rats. METHODS: Mature rats were dissected and the relative positions, dimensions, and weights of all of their major organs were measured. A mathematic model was set up for the rat body and its internal organs to enable Monte Carlo radiation transport calculations to determine estimates for both tumor and organ self-doses as cross-organ doses for (90)Y, (111)In, and (177)Lu. The organs and body were mostly of ellipsoid shape with the axes given as the measured length, width, and height normalized to values that, together with the measured weights, are consistent with the recommended soft-tissue and bone densities. A spheric tumor of 0.25 g was positioned on the right femur. Calculations were performed with the Monte Carlo neutral particle transport code MCNP for the beta-emitters (maximum energy, 2.28 MeV) and (177)Lu (maximum energy, 0.497 MeV) and for the gamma-emissions from (177)Lu and from (111)In. The presented absorbed dose S values are used to calculate the absorbed dose estimates for the rat organs in a study on the biodistribution of (177)Lu-DOTA-Tyr(3)-octreotate (DOTA is 1,4,7,10-tetraazadodecane-N,N',N",N"'-tetraacetic acid). Three activity distributions were considered in the kidney: uniform in the whole kidney, in the cortex, or in the outer 1-mm-thick rim of the cortex. Isodose curves and dose volume histograms were calculated for the dose distribution to the kidneys. RESULTS: Depending on the activity distribution in the kidneys, the renal dose for (177)Lu-DOTA-Tyr(3)-octreotate is 0.13-0.17 mGy/MBq. CONCLUSION: The renal dose of 70-95 Gy for an injected activity of 555 MBq will likely cause radiation damage, although the higher amount of peptide with this activity may influence the dosimetry by partial receptor saturation. Dose volume histograms show that (111)In and (177)Lu are likely to have a higher threshold for renal damage than (90)Y.

Transport of octreotide and evaluation of mechanism of opening the paracellular tight junctions using superporous hydrogel polymers in Caco-2 cell monolayers.

The purpose of this study was to investigate the mechanism of opening of tight junctions in Caco-2 cell monolayers using superporous hydrogel (SPH) and SPH composite (SPHC) polymers as permeation enhancers for peptide drug delivery. Moreover, the transport of octreotide across Caco-2 cell monolayers was assessed by application of SPH and SPHC polymers on Caco-2 cell monolayers. In these experiments, N,N,N-trimethyl chitosan chloride with 60% quaternization (TMC60) was used as a positive control for opening of tight junctions. Transepithelial electrical resistance (TEER) studies showed that all three polymers (TMC60, SPH, and SPHC) were able to decrease TEER values to approximately 30% of the initial values, indicating the ability of these polymers to open the tight junctions. Recovery TEER studies showed that the effects of the polymers on Caco-2 cell monolayers were reversible, indicating viability of the cells after incubation with polymers. Both SPH and SPHC (compared with TMC60) were able to increase the paracellular transport of octreotide by their mechanical pressures on tight junctions. The mechanistic studies showed that junctional proteins, including actin, occludin, and claudin-1, were influenced by application of SPH and SPHC polymers to the Caco-2 cell monolayers. SPH and SPHC induced clear changes in the staining pattern of all three proteins compared with the control, indicating that the expression of these proteins in the tight junctions was increased, most likely due to the mechanical pressure of the polymers on the junctional proteins.

DOTA-NOC, a high-affinity ligand of somatostatin receptor subtypes 2, 3 and 5 for labelling with various radiometals.

Earlier studies have shown that modification of the octapeptide octreotide in positions 3 and 8 may result in compounds with increased somatostatin receptor affinity that, if radiolabelled, display improved uptake in somatostatin receptor-positive tumours. The aim of a recent research study in our laboratory was to employ the parallel peptide synthesis approach by further exchanging the amino acid in position 3 of octreotide and coupling the macrocyclic chelator DOTA(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to these peptides for labelling with radiometals like gallium-67 or -68, indium-111, yttrium-90 and lutetium-177. The purpose was to find radiopeptides with an improved somatostatin receptor binding profile in order to extend the spectrum of targeted tumours. A first peptide, [111In,90Y-DOTA]-1-Nal3-octreotide (111In,90Y-DOTA-NOC), was isolated which showed an improved profile. InIII-DOTA-NOC exhibited the following IC50 values (nM) when studied in competition with [125I][Leu8, d-Trp22, Tyr25]somatostatin-28 (values for YIII-DOTA-NOC are shown in parentheses): sstr2, 2.9 +/- 0.1 (3.3 +/- 0.2); sstr3, 8 +/- 2 (26 +/- 1.9); sstr5, 11.2 +/- 3.5 (10.4 +/- 1.6). Affinity towards sstr1 and 4 was very low or absent. InIII-DOTA-NOC is superior to all somatostatin-based radiopeptides having this particular type of binding profile, including DOTA-lanreotide, and has three to four times higher binding affinity to sstr2 than InIII,YIII-DOTA-Tyr3-octreotide (InIII,YIII-DOTA-TOC). In addition, [111In]DOTA-NOC showed a specific and high rate of internalization into AR4-2J rat pancreatic tumour cells which, after 4 h, was about two times higher than that of [111In]DOTA-TOC and three times higher than that of [111In]DOTA-octreotide ([111In]DOTA-OC). The internalized radiopeptides were externalized intact upon 2 h of internalization followed by an acid wash. After 2-3 h of externalization a plateau is reached, indicating a steady-state situation explained by reactivation of the receptors followed by re-endocytosis. Biodistribution studies in CA 20948 tumour-bearing rats showed rapid clearance from all sstr-negative tissues except the kidneys. At 4 h the uptake of [111In]DOTA-NOC in the tumour and sstr-positive tissues, such as adrenals, stomach and pancreas, was three to four times higher than that of [111In]DOTA-TOC. Differential blocking studies indicate that this is at least partially due to the uptake mediated by sstr3 and sstr5. These very promising preclinical data justify the use of this new radiopeptide for imaging and potentially internal radiotherapy studies in patients.

Population pharmacodynamic analysis of octreotide in acromegalic patients.

INTRODUCTION: Octreotide is an octapeptide analog of somatostatin used to normalize growth hormone levels in acromegaly. This article presents a population analysis of the relationship between octreotide and growth hormone concentrations in 94 patients with acromegaly, including 10 patients responding incompletely to subcutaneous treatment (poor responders). METHODS: Growth hormone and octreotide concentrations were recorded hourly over 12-hour time periods during long-term subcutaneous treatment. Twelve-hour profiles were also collected on different days up to 2 months after intramuscular injection of the long-acting formulation. We modeled the inhibition of growth hormone secretion by octreotide with a direct maximum inhibition model. A joint analysis of both formulations was performed with NONMEM (GloboMax, LLC, Hanover, Md). During model building, we examined the relationships between parameters and demographic covariates or formulations with the use of likelihood ratio tests. RESULTS: The baseline growth hormone level was higher in poor responders and was best described by a bimodal distribution. The maximum inhibition was common to both formulations and had a mean of 90%, with low interindividual variability. Sensitivity to octreotide (50% inhibitory concentration) was found to be slightly lower on average with intramuscular administration than with subcutaneous administration. CONCLUSION: Given adequate doses of octreotide, in 72% of 94 patients, growth hormone would decrease to levels below 2.5 ng. mL(-1), considered to be a desirable target concentration in acromegaly. This study provides a way to identify poor responders during subcutaneous treatment, allowing an early clinical decision to be made to switch nonresponders to alternative therapies.

PET imaging of somatostatin receptors: design, synthesis and preclinical evaluation of a novel 18F-labelled, carbohydrated analogue of octreotide.

Because of the excellent nuclear properties of fluorine-18 and the growing interest in somatostatin receptor (sst) scintigraphy with PET, a novel carbohydrated (18)F-labelled sst ligand was developed and preclinically evaluated. Synthesis of N(alpha)-(1-deoxy- D-fructosyl)- N(epsilon)-(2-[(18)F]fluoropropionyl)-Lys(0)-Tyr(3)-octreotate ([(18)F]FP-Gluc-TOCA) was completed in approximately 3 h (20%-30% yield). [(19)F]FP-Gluc-TOCA showed no affinity to hsst1 and hsst3, moderate affinity to hsst4 (IC(50): 437+/-84 n M) and hsst5 (IC(50): 123+/-8.8 n M) and very high affinity to hsst2 (IC(50): 2.8+/-0.4 n M). As a result of carbohydration, lipophilicity of [(18)F]FP-Gluc-TOCA was found to be low (lg P(OW)=-1.70+/-0.02). In mice, the tracer was rapidly cleared via renal excretion (kidneys: 8.69%+/-1.09%ID/g) and showed low uptake in liver (0.72%+/-0.14%ID/g) and intestine (1.88%+/-0.52%ID/g) and high tumour uptake (13.54%+/-1.47%ID/g) (all data at 1 h p.i.). Tumour to non-tumour ratios at 60 min p.i. reached 25, 19, 7, 1.6 and 56 for blood, liver, intestine, kidney and muscle, respectively. A similar biodistribution pattern was observed in pancreatic tumour-bearing rats. Tumour uptake in rats was reduced to 36% and 18% of control (30 and 60 min) by co-injection of 500 microg Tyr(3)-octreotide, demonstrating sst-specific uptake. In a first [(18)F]FP-Gluc-TOCA-PET study of a patient with a metastatic carcinoid in the liver the tracer showed superior pharmacokinetics, e.g. rapid urinary excretion and low uptake in liver, kidney and spleen. Multiple liver lesions (SUVs ranging from 21.4 to 38.0) and previously unknown focal uptake in the abdomen (SUV 10.0) were clearly visible. This is the first report on PET imaging using an (18)F-labelled sst binding peptide; it indicates that [(18)F]FP-Gluc-TOCA offers excellent imaging characteristics and allows sst imaging with high tumour to non-tumour contrast.

[(123)I]metaiodobenzylguanidine and [(111)In]octreotide uptake in begnign and malignant pheochromocytomas.

Selecting the appropriate approach for resection and follow-up of pheochromocytomas (PCCs) is highly dependent upon reliable localization and exclusion of multifocal, bilateral, or metastatic disease. Metaiodobenzylguanidine (MIBG) scintigraphy was developed for functional localization of catecholamine-secreting tissues. Somatostatin receptor imaging (SRI) has a high sensitivity for localizing head and neck paragangliomas, but studies of intraabdominal PCCs are rare. In this study we review our experience of [(123)I]MIBG and SRI, performed since 1983 and 1989, respectively, in the work-up of primary and recurrent PCCs. Scintigraphic results were correlated with catecholamine secretion, size and site, malignancy, associated tumor syndromes, and morphological features. [(123)I]MIBG scans were performed in a total of 75 patients, in 70 cases before resection of primary PCCs and in 5 cases because of recurrent disease. Ninety-one PCCs were resected. The overall detection rates were 83.3% and 89.8% for PCCs larger than 1.0 cm. Multifocal disease was detected in 4 patients with [(123)I]MIBG. [(123)I]MIBG uptake correlated with greater size of PCC (r = 0.33; P = 0.008) and greater concentration of plasma epinephrine (r = 0.32; P = 0.006). [(123)I]MIBG-negative PCCs (n = 14) had significantly (P = 0.01) smaller diameters than [(123I)]MIBG-positive tumors. Furthermore, [(123)I]MIBG uptake was significantly higher in unilateral (P = 0.02), benign (P = 0.02), sporadic (P = 0.02), intraadrenal (P = 0.02), and capsular invasive (P = 0.03) PCCs than in bilateral, malignant, MEN2A/2B-related, extraadrenal, and noninvasive PCCs, respectively. The detection rate of SRI was only 25% (8 of 32) for primary benign PCCs. In 14 patients metastases occurred, which were effectively visualized with [(123)I]MIBG in 8 of 14 cases. SRI was able to detect metastases in 7 of 8 cases, including 3 [(123)I]MIBG-negative metastatic cases. In addition, [(123)I]MIBG and SRI detected 2 recurrences. In conclusion, [(123)I]MIBG uptake is correlated with the size, epinephrine production, and site of PCCs. Its role in bilateral and MEN2A/2B-related PCCs seems limited. In cases of recurrent elevation of catecholamines, localization of metastases and/or recurrence should be attempted with [(123)I]MIBG scintigraphy. In suspicious metastatic PCCs, SRI might be considered to supplement [(123)I]MIBG scintigraphy.